ACOX2

ACOX2 Full Name

acyl-CoA oxidase 2, branched chain

ACOX2 Introduction

Acyl-CoA Oxidase 2 (ACOX2) is a key peroxisomal enzyme belonging to the acyl-CoA oxidase family, which is specifically responsible for the initial step in the β-oxidation of branched-chain fatty acids (BCFAs) and bile acid intermediates within peroxisomes. Peroxisomes are essential organelles involved in the metabolism of lipids that cannot be degraded in mitochondria, and ACOX2 plays a unique role in breaking down branched-chain acyl-CoA esters—such as pristanoyl-CoA and branched-chain bile acid intermediates—that are derived from dietary sources or endogenous synthesis. Unlike other acyl-CoA oxidase isoforms that target straight-chain fatty acids, ACOX2 is specialized in branched-chain substrates, making it indispensable for maintaining peroxisomal lipid homeostasis and preventing the accumulation of toxic branched-chain lipid intermediates. ACOX2 is primarily expressed in tissues with high peroxisomal activity, including the liver, kidney, and brain, and its functional integrity is critical for normal lipid metabolism and overall cellular health. Today, ACOX2 is recognized not only as a specialized peroxisomal enzyme but also as a key gene associated with peroxisomal disorders, with profound implications for lipid biology, peroxisome research, and clinical genetics.

Figure 1.The structure of ACOX2.

ACOX2 Gene and Protein Features
ACOX2 is a central component of the peroxisomal branched-chain fatty acid β-oxidation pathway, which is critical for the degradation of branched-chain fatty acids (such as pristanic acid and phytanic acid) and the biosynthesis of bile acids. Pristanic acid, a branched-chain fatty acid derived from dietary dairy products and meat, is transported to peroxisomes and converted to pristanoyl-CoA, which is then oxidized by ACOX2 to initiate its degradation. Similarly, ACOX2 participates in the degradation of branched-chain bile acid intermediates, such as dihydroxycholestanoic acid (DHCA) and trihydroxycholestanoic acid (THCA), which are produced during bile acid synthesis in the liver. By facilitating the breakdown of these substrates, ACOX2 prevents their accumulation in cells, which would otherwise be toxic and disrupt cellular function. Additionally, the β-oxidation of branched-chain fatty acids by ACOX2 generates acetyl-CoA and propionyl-CoA, which can be further metabolized in the mitochondria to generate energy. Thus, ACOX2 links peroxisomal lipid metabolism to cellular energy production, contributing to overall metabolic homeostasis.

ACOX2 in Disease and Therapeutic Relevance
Genetic mutations in the ACOX2 gene are associated with rare inherited peroxisomal disorders, primarily pristanoyl-CoA oxidase deficiency (PCOD), an autosomal recessive disorder characterized by the impaired degradation of branched-chain fatty acids. Patients with PCOD exhibit elevated levels of pristanic acid and branched-chain bile acid intermediates in the blood and tissues, leading to a range of clinical manifestations, including neurological abnormalities (such as developmental delay, seizures, and peripheral neuropathy), hepatic dysfunction, and skeletal abnormalities. In severe cases, PCOD can be life-threatening in early childhood if left untreated. Beyond inherited disorders, ACOX2 dysregulation has been implicated in other pathological conditions, including non-alcoholic fatty liver disease (NAFLD) and peroxisomal dysfunction associated with aging. Reduced ACOX2 activity in the liver can lead to the accumulation of branched-chain fatty acids, contributing to hepatic steatosis and inflammation. ACOX2 also holds therapeutic relevance, as targeting its activity could potentially treat peroxisomal disorders and metabolic diseases associated with branched-chain lipid accumulation. Currently, diagnostic testing for ACOX2 mutations is available for patients with suspected peroxisomal disorders, and research is ongoing to develop targeted therapies to restore ACOX2 function.

Alternate Names for ACOX2

ACOX2; acyl-CoA oxidase 2, branched chain; acyl Coenzyme A oxidase 2, branched chain; peroxisomal acyl-coenzyme A oxidase 2; BRCACOX; BRCOX; THCA-CoA oxidase; trihydroxycoprostanoyl-CoA oxidase; acyl-Coenzyme A oxidase 2, branched chain; peroxisomal branched chain acyl-CoA oxidase